Semiconductor device and manufacturing method thereof

ABSTRACT

In a method for manufacturing a semiconductor device, a first dielectric layer is formed over a substrate, first recesses are formed in the first dielectric layer. Metal wirings extending is a first direction are formed in the first recesses. A mask layer is formed over the metal wirings and the first dielectric layer, which includes a first opening extending in the first direction and is located above a space between adjacent two metal wirings. A first groove corresponding to the first opening is formed between the adjacent two metal wirings by etching the first dielectric layer using the mask layer as an etching mask. A second dielectric layer is formed so that a first air gap is formed in the first groove. A width of the first opening in a perpendicular direction to the first direction is smaller than a space between the adjacent two metal wirings.

RELATED APPLICATION

This application is a Continuation Application of U.S. Ser. No.15/157,159, filed May 17, 2016, which claims priority to U.S.Provisional Application No. 62/273,387 filed on Dec. 30, 2015, theentire contents of which applications are incorporated herein byreference.

TECHNICAL FIELD

The disclosure relates to a semiconductor integrated circuit, moreparticularly to a semiconductor device having air gaps between metalwirings and its manufacturing process.

BACKGROUND

As the semiconductor industry introduces new generations of integratedcircuits (ICs) having higher performance and greater functionality, thedensity of the elements that form the ICs is increased, while thedimensions and spacing between components or elements of the ICs arereduced, which causes a variety of problems. For example, for any twoadjacent conductive features, when the distance between the conductivefeatures decreases, the resulting capacitance (parasitic capacitance)increases. The increased capacitance results in an increase of powerconsumption and an increase in the resistive-capacitive (RC) timeconstant, i.e., an increase of signal delays. The capacitance betweentwo adjacent conductive features (e.g., metal wirings) is a function ofthe dielectric constant (k value) of an insulating material filled inthe space between the conductive features (also, a function of adistance between the conductive features and a size of the side surfacesof the conductive features). Therefore, the continual improvement insemiconductor IC performance and functionality is dependent upondeveloping insulating (dielectric) materials with low k values. Sincethe substance with the lowest dielectric constant is air (k=1.0),air-gaps are formed to further reduce the effective k value of metalwiring layers.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1-11 show exemplary sequential processes for manufacturing asemiconductor device having air gaps according to one embodiment of thepresent disclosure.

FIG. 12 shows a comparative example of a semiconductor device having airgaps.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.”

FIGS. 1-11 show exemplary sequential processes for manufacturing asemiconductor device having air gaps according to one embodiment of thepresent disclosure. FIGS. 1-11 illustrate exemplary sequential processesfor fabricating one of metal wiring layers (wiring levels), which areformed above a substrate. Although there are core structures such astransistors or other elements (e.g., contacts etc.) constituting thesemiconductor device (hereinafter referred to as “underlyingstructures”) between the substrate and the metal wiring layers, detailedillustrations of such elements are omitted in FIGS. 1-11 for simplicity.The order of the processes may be changed. FIGS. 1-3, 5A, 6A, . . . 10Aand 11 show exemplary cross sectional views and FIGS. 5B, 6B, . . . 10Bshow exemplary plan views (top views).

As shown in FIG. 1, a first interlayer dielectric (ILD) layer 10 isformed over the underlying structures 5 disposed over the substrate 1.An interlayer dielectric layer may also be called an inter-metaldielectric (IMD) layer. The first ILD layer 10 is made of, for example,one or more layers of low-k dielectric material. Low-k dielectricmaterials have a k-value (dielectric constant) lower than about 4.0.Some low-k dielectric materials have a k-value lower than about 3.5 andother low-k dielectric material may have a k-value lower than about 2.5.

The materials for the first ILD layer 10 include compounds comprisingelements of Si, O, C and/or H, such as SiCOH and SiOC. Organicmaterials, such as polymers, may be used for the first ILD layer 10. Forexample, the first ILD layer 10 is made of one or more layers of acarbon-containing material, organo-silicate glass, a porogen-containingmaterial, and/or combinations thereof. Nitrogen may also be included inthe first ILD layer 10 in some embodiments. The first ILD layer 10 maybe a porous layer. The density of the first ILD layer 10 is less thanabout 3 g/cm³ in one embodiment and may be less than about 2.5 g/cm³ inother embodiments. The first ILD layer 10 may be formed by using, forexample, plasma-enhanced chemical vapor deposition (PECVD), low pressureCVD (LPCVD), atomic layer CVD (ALCVD), and/or a spin-on technology. Incase of PECVD, the film is deposited at a substrate temperature in arange of about 25° C. to about 400° C. and at a pressure of less than100 Torr.

In some embodiments, the first ILD layer includes an inter-layerinsulating film and an inter-wire insulating film such that the metalwirings will be formed mainly in the inter-metal insulating film. Theinter-layer insulating film may include a SiOC film and the inter-wireinsulating film may include a TEOS (tetraethylorthosilicate) film.

In some embodiments, an under-layer etch-stop layer (ESL) 20 is formedover the first ILD layer 10, and an under-layer cap layer 30 is formedover the under-layer ESL 20. The under-layer ESL 20 includes one or morelayers of SiN, SiCO, SiON, SiCN, and SiCON. The under-layer cap layer 30includes one or more layers of a silicon oxide based material, suchSiO₂, TEOS and SiON in some embodiments.

Further, a second ILD layer 50 is formed over the first ILD layer 10 orthe under-layer cap layer 30, if under-layer cap layer 30 is used. Thematerial for the second ILD layer 50 is selected from the exemplarymaterials for the first ILD layer 10 as set forth above.

As shown in FIG. 2, first recesses 15 are formed in the second ILD layer50 by using patterning operations including lithography and etchingprocesses. In some embodiments, one or more via holes (contact holes)(not shown) to be connected to one or more elements of the underlyingstructures are formed at the bottom of the first recesses.

As shown in FIG. 3, a metal material is formed in the first recesses toform metal wirings 100, 102, 104 and 106. The operations to form themetal wirings include a damascene process. In the damascene process, oneor more layers of metal material are formed in the first recesses 15 andthe upper surface of the second ILD layer 50, and a planarizationoperation such as a chemical mechanical polishing method and/or aetch-back method is performed to remove portions of the metal materialformed on the upper surface of the second ILD layer 50.

As shown in FIG. 3, the semiconductor device of the present embodimentincludes a dense wiring region A1 and a coarse wiring region A2. In thedense wiring region A1, the metal wirings 100, 102 and 104 are arrangedwith a space S1, and in the coarse wiring region A2, the metal wirings104 and 106 are arranged with a space S2, where S2>S1. In FIG. 3, thewiring 104 belongs to the dense wiring region A1 and the coarse wiringregion A2 for the purpose this disclosure. In other embodiments, thedense wiring region A1 and the coarse wiring region A2 are not adjacentto each other and do not share the same wiring. The metal wiring 106 inthe coarse wiring region A2 may be a dummy metal wiring, which is not apart of a functioning circuit. In FIG. 3, the metal wirings extend inthe Y direction.

In one embodiment, the space S1 is the minimum space Smin for the metalwirings in this layer, which is defined by the design rule. In otherwords, no two metal wirings in the same wiring layer are arranged with aspace smaller than Smin within one semiconductor device. Generally oneminimum space Smin value for one metal wiring layer is defined withinone semiconductor device, and the value of Smin may be different inother wiring layers or in other devices.

In some embodiments, S1 is in a range from about 10 nm to about 38 nm.Further, in the dense wiring region A1, the line width W1 of the metalwirings is substantially the same as S1, in some embodiments. In otherembodiments, the dense wiring region A1 is defined as a region in whichmetal wirings are arranged with S1, where Smin≦S1<αSmin (1<α<3, forexample, 1.2, 1.5, 2.0, 2.5, etc). Air gaps are subsequently formed inthe dense wiring region A1.

In contrast, in the coarse wiring region A2, the space S2 betweenadjacent metal wirings is set larger than S1. The space S2 varies in thesemiconductor device depending on, for example, the locations and thefunctions of the metal wirings. In one embodiment, the space S2 issimply greater than S1. In certain embodiments, when S1=Smin, S2 isgreater than Smin, and when Smin≦S1<αSmin, S2 is equal to or greaterthan αSmin. In other embodiments, Smin≦S1≦αSmin and S1<S2.

The one or more layers of metal material for the metal wirings 100, 102,104 and 106 are formed by CVD, physical vapor deposition (PVD) includingsputtering and/or electro-plating.

The metal material for the metal wirings is one or more layers of Al,Cu, Co, Mn, W, Ti, Ta, TiN, TaN, TiW, WN, TiAl, TiAlN, TaC, TaCN andTiSiN. For example, the metal wirings may include a barrier layer 90made of, for example, TiN and/or TaN, and a body layer (100, 102, 204and 106) made of, for example, Cu or Cu-based materials. The metalwiring structure may be made by a damascene process.

After forming the metal wirings 100, 102, 104 and 106, a first etch-stoplayer (ESL) 200 is formed over the metal wirings and the second ILDlayer 50, as shown in FIG. 4A. The first ESL 200 functions as an etchingmask layer in a subsequent etching of the second ILD layer 50. The firstESL 200 includes one or more layers of a Si-based insulating materialcontaining Si with O, N, C, B and or H, or an Al-based insulatingmaterial containing Al with O, N, C, B and or H. Examples of the secondetch-stop layer include SiN, SiCO, SiCN and SiCON. In one embodiment,SiN is used.

The thickness of the first ESL 200 is in a range of about 1 nm to about30 nm in some embodiments, and is in a range of about 5 nm to about 15nm in other embodiments. The density of the first ESL 200 is less thanabout 3 g/cm³ in one embodiment and may be less than about 2.5 g/cm³ inother embodiments.

The first ESL 200 may be formed by using, for example, PECVD, LPCVD,ALCVD, and/or a spin-on technology. In case of PECVD, the first ESL 200is deposited at a substrate temperature in a range of about 25° C. toabout 400° C. and at a pressure of less than 100 Torr.

After the formation of the first ESL 200, a first mask layer 210 isformed on the first ESL 200, and a second mask layer 220 is formed onthe first mask layer 210, as shown in FIG. 4A. The first mask layer 210is made of, for example, an organic material, such as a material used asa bottom anti-reflection coating (BARC). The second mask layer 220 ismade of a material having a high degree of etching selectivity to thefirst mask layer 210, and is made of an organic material with a high Sicontent different from the first mask layer 210. The content of Si inthe organic material is about 30 weight % or more. The thickness of thefirst mask layer 210 is in a range of about 50 nm to about 200 nm insome embodiments, and the thickness of the second mask layer 220 is in arange of about 20 nm to about 50 nm in some embodiments.

Further, as shown in FIG. 4A, a photo resist pattern 230 having a firstopening 235 and a second opening 237 is formed on the stacked layers ofthe first ESL 200, the first mask layer 210 and the second mask layer220. Edges of the longer sides (along the Y direction) of the openings235 and 227 are located over the upper surfaces of or the edges of theadjacent metal wirings in plan view, as shown in FIG. 4B. In otherwords, the first opening 235 is partially overlapped with at least oneof the metal wirings 100 and 102.

By using the photo resist pattern 230 as an etching mask, the secondmask layer 220 is patterned, and subsequently, the first mask layer 210is patterned. In the patterning the first mask layer, the photo resistpattern 230 is used as an etching mask, or the patterned second masklayer 220 is used as an etching mask after the photo resist pattern isremoved. After the photo resist pattern and the second mask layer areremoved, the first mask layer having a first opening 215 and a secondopening 217 as shown in FIGS. 5A and 5B is obtained. As shown in FIG.5A, a crosslinked layer 212 of organic material is formed on thepatterned first mask layer 210, in some embodiments. Depending on thematerials of the first and second mask layers, the crosslinked layer maynot be formed.

After the patterning of the first mask layer 210, the width W1 in the Xdirection of the first and second openings 215, 217 is equal to orgreater than a space S1 of the adjacent two metal wirings (at the uppersurface) e.g., wirings 100 and 102, or wirings 102 and 104. Edges of thelonger sides (along the Y direction) of the openings 215 and 217 arelocated over the upper surfaces of or the edges of the adjacent metalwirings in plan view, as shown in FIG. 5B. In other words, the firstopening 215 is partially overlapped with at least one of the metalwirings 100 and 102. When the space width between adjacent two metalwirings is S and the line width of the metal wirings is L, the width ofthe openings is less than about S+L, where the center of the openings islocated above the space between adjacent two metal wirings, so that thefirst opening 215 and the second opening 217 are separated.

Subsequently, an operation to reduce the width of the first opening 215and the second opening 217 is performed. As shown in FIGS. 6A and 6B, ablanket spacer layer 300 is formed over the structure of FIGS. 5A and5B. The blanket spacer layer 300 includes an oxide material, such asTiO₂ or ZrO₂, or a nitride material, such as TiN or TaN. In thisembodiment, TiO₂ is used as the blanket spacer layer 300. The thicknessof the blanket spacer layer 300 is in a range from about 3 nm to about10 nm in some embodiments.

An anisotropic etching is performed on the blanket spacer layer 300,thereby forming a first sidewall spacer 312 on a sidewall of the firstopening 215 and a second sidewall spacer 314 on a sidewall of the secondopening 217, so that a second mask pattern having a reduced firstopening 215′ defined by the first sidewall spacer 312 and a reducedsecond opening 217′ defined by the second sidewall spacer 314 areobtained, as shown in FIGS. 7A and 7B.

The width W2 of the reduced first opening 215′ is smaller than the spaceS1 between the adjacent two metal wirings, and is in a range from about5 nm to about 10 nm in some embodiments. Further, the reduced firstopening 215′ does not overlap the underlying metal wirings 100 and 102,in plan view. The configuration of the reduced second opening 217′ issubstantially the same as that of the reduced first opening 215′.

In some embodiments, a resist pattern having the reduced width W2 as thesecond mask pattern is formed on the first ESL 200 by using ahigh-resolution lithography tool, such as an e-beam lithography systemor an EUV or X-ray lithography system.

As shown in FIGS. 8A and 8B, the first ESL 200 is patterned by anetching operation using the second mask as an etching mask, therebyforming openings 215″ and 217″ in the first ESL 200, corresponding tothe first reduced opening 215′ and the second reduced opening 217′,respectively. The width of the openings 215″ and 217″ is substantiallythe same as the width of the first reduced opening 215′ and the secondreduced opening 217′. By this etching a part of the upper surface of thesecond ILD 200 is exposed at the bottoms of openings 215″ and 217″.

As shown in FIGS. 9A an 9B, a first groove 52 corresponding to theopening 215″ and a second groove 54 corresponding to the opening 217″are formed between adjacent two metal wirings (100 and 102, 102 and 104)by etching the second ILD 50 through the openings 215″ and 217″.

In one embodiment, the stack of the patterned first ESL 200 and firstmask layer 210 with sidewall spacers is used as an etching mask, asshown in FIGS. 9A and 9B. The etching of the second ILD 50 includes adry etching and/or a wet etching, followed by a wet cleaning process. Insome embodiments, the first mask layer 210 with sidewall spacers isremoved and only the patterned first ESL 200 is used as an etching maskin other embodiments. The maximum width W3 of the first groove 52 in theX direction is in a range from about 15 nm to about 20 nm in someembodiments. The depth H1 of the first groove 52 in the Z direction isin a range from about 70 nm to about 120 nm in some embodiments. Thebottom of the first groove 52 may be located below the bottom of themetal wirings. The second groove 54 has substantially the sameconfiguration as the first groove 52.

After the second ILD 50 is etched to form the first and second grooves,the first mask layer 210 with the sidewall spacers is removed, as shownin FIG. 10A and 10B.

As shown in FIG. 10A and 10B, upper surfaces of two metal wirings 100and 102 adjacent to the first groove 52 are covered by the mask layerand are not exposed. Similarly, upper surfaces of two metal wirings 102and 104 adjacent to the first groove 54 are covered by the mask layerand are not exposed. The first ESL 200 includes a portion overhangingthe first groove 52 and a portion overhanging the second groove 54. Theamount of the overhanging L1 is in a range from about 0.5 nm to about 2nm in some embodiments.

After the grooves are formed and the first mask layer 210 with thesidewall spacers is removed, a dielectric layer for forming air gaps 56,58 is formed in and over the grooves. The dielectric layer includes twoor more layers of dielectric material.

In some embodiments, as shown in FIG. 11, the dielectric layer includesa second ESL 240, a cap layer 230 and a third ILD 150. The second ESL240 is conformally formed on inner surface of the first and secondgrooves 52, 54. In some embodiments, the cap layer 230 is alsoconformally formed on the second ESL 240. The third ILD 150 is notsubstantially formed in the grooves as the cap layer 230 makes the upperopening of the groove very small. Thus, a part of the cap layer 230 inthe first and second grooves is not covered by the third ILD 150. Insome embodiments, the cap layer 230 completely closes the upper openingsof the grooves.

As shown in FIG. 11, the thickness of the second ESL 240 formed in thegrooves is smaller than the thickness of the second ESL formed over thefirst ESL 220. Similarly, the thickness of the cap layer 230 formed inthe grooves is smaller than the thickness of the cap layer formed abovethe first ESL 220. Accordingly, it is possible to make the volume of theair gaps 56, 58 large. In some embodiments, the air gap 56 replaces morethan ⅔ of the volume of the area between adjacent two metal wirings. Inthe cross sectional view of FIG. 11, the air gap area of air gap 56 ismore than ⅔ of the trapezoid area TR between metal wirings 100 and 102.

The second ESL 240 includes one or more layers of SiN, SiCO, SiCN andSiCON. In one embodiment, SiN is used. The thickness of the second ESL240 is in a range from about 5 nm to about 15 nm in some embodiments.The cap layer 230 includes one or more layers of a silicon oxide basedmaterial, such SiO₂, TEOS and SiON. In one embodiment, TEOS is used. Thethickness of the cap layer 230 is in a range from about 5 nm to about 15nm in some embodiments.

To form air gaps by the third ILD layer 150, a non-conformal CVD methodwith a low step coverage condition may be utilized. By usingnon-conformal CVD, the deposited third ILD at the openings of thegrooves “pinch-off” (is connected) before the grooves are filled withthe insulating material of the third ILD layer, thereby forming air gapsin the grooves.

The third ILD layer 150 may include one or more layers of silicon oxide,silicon oxynitride (SiON), SiCN, SiOC or SiOCN, or low-k material. Thethird ILD layer 150 may be doped with, for example, phosphorous, toenhance its void formation effects.

FIG. 12 shows a comparative example, in which a mask pattern(corresponding to the second mask pattern for etching the second ILD)having a wider opening that covers two spaces formed by three wiringpatterns is used. In the comparative example, when the second ILD 50 isetched, at last part of the upper surface of the metal wirings 100, 102and 104 are exposed and etched, thereby forming rounded corner shapes.The residue of the etched metal (e.g., Cu) from the metal wirings mayremain in the grooves, which may require an additional cleaningoperation. Further, it may be necessary to compensate for the etchedmetal wirings by depositing an additional metal material (e.g., Co) toprevent erosion of the upper surface of the metal wirings. Further, theregion where the air gaps are formed has a low-height topography,compared with the other regions where no air gap is formed.

In contrast, in the present embodiments, since the upper surfaces of themetal wirings are protected by the first ESL 200, the upper corners ofthe metal wirings can maintain an acute angle and no rounding isobserved. Further, the stacked layers of the first ESL 200, the secondESL 240 and the cap layer 230 are disposed over the metal wirings, it ispossible to maintain the same height after a planarization operation(e.g., a chemical mechanical polishing) of the third ILD. Moreover, thefirst ESL formed on the metal wiring (e.g., Cu) can prevent erosion ofthe Cu layer. In addition, because a lower amount of the cap layer (andthe third ILD) is filled in the groove, it is possible to increase thevolume of the air gaps.

The various embodiments or examples described herein offer severaladvantages over the existing art, as set forth above. It will beunderstood that not all advantages have been necessarily discussedherein, no particular advantage is required for all embodiments orexamples, and other embodiments or examples may offer differentadvantages.

In accordance with one aspect of the present disclosure, in a method formanufacturing a semiconductor device, a first dielectric layer is formedover a substrate. First recesses are formed in the first dielectriclayer. Metal wirings are formed in the first recesses. The metal wiringsextend in a first direction. A mask layer is formed over the metalwirings and the first dielectric layer. The mask layer includes a firstopening extending in the first direction, and is located above a spacebetween adjacent two metal wirings. A first groove corresponding to thefirst opening is formed between the adjacent two metal wirings byetching the first dielectric layer using the mask layer as an etchingmask. A second dielectric layer is formed so that a first air gap isformed in the first groove. A width of the first opening in a seconddirection perpendicular to the first direction is smaller than a spacebetween the adjacent two metal wirings in the second direction.

In accordance with another aspect of the present disclosure, in a methodfor manufacturing a semiconductor device, a first dielectric layer isformed over a substrate. First recesses are formed in the firstdielectric layer. Metal wirings are formed in the first recesses. Themetal wirings extend in a first direction. A first insulating layer isformed over the metal wirings and the first dielectric layer. A firstmask pattern is formed over the first insulating layer. The first maskpattern includes a first opening extending in the first direction andhaving a width in a second direction perpendicular to the firstdirection. The width of the first opening is reduced, thereby forming asecond mask pattern having a second opening with a smaller width thanthe first opening. The first insulating layer is patterned by using thesecond mask as an etching mask, thereby forming a third opening in thefirst insulating layer corresponding to the second opening. A firstgroove corresponding to the third opening is formed between adjacent twometal wirings by etching the first dielectric layer through the thirdopening. A second dielectric layer is formed so that a first air gap isformed in the first groove. A width of the third opening in the seconddirection is smaller than a space between the adjacent two metal wiringsin the second direction.

In accordance with another aspect of the present disclosure, asemiconductor device includes a first dielectric layer disposed over asubstrate, metal wirings, a second dielectric layer, an insulating layerand an air gap. The metal wirings are embedded in the first dielectriclayer, and extend in a first direction. The second dielectric layer isdisposed over the first dielectric layer and the metal wirings. Theinsulating layer is disposed between the first dielectric layer and thesecond dielectric layer. The air gap is formed between adjacent twometal wirings. Upper surfaces of the adjacent two metal wirings arefully covered by the first insulating layer and are not in contact withthe second dielectric layer. The first insulating layer overhangs aspace between adjacent two metal wirings.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method for manufacturing a semiconductordevice, comprising: forming metal wirings embedded in a first dielectriclayer, the metal wirings including a first metal wiring, a second metalwiring and a third metal wiring, all extending in a first direction andarranged in a second direction perpendicular to the first direction;forming a mask layer over the metal wirings and the first dielectriclayer, the mask layer including a first opening and a second opening,both extending in the first direction, the first opening being locatedabove a space between the first metal wiring and the second metalwiring, the second opening being located above a space between thesecond metal wiring and the third metal wiring, the first opening beingseparated from the second opening; forming a first groove correspondingto the first opening between the first metal wiring and the second metalwiring and a second groove corresponding to the second opening betweenthe second metal wiring and the third metal wiring by etching the firstdielectric layer using the mask layer as an etching mask; and forming asecond dielectric layer so that a first air gap is formed in the firstgroove and a second air gap is formed in the second groove, wherein awidth of the first opening in the second direction is smaller than aspace between the first metal wiring and the second metal wiring in thesecond direction.
 2. The method of claim 1, wherein after the formingthe first and second grooves, upper surfaces of the first metal wiring,the second metal wiring and the third metal wiring are covered by themask layer and are not exposed.
 3. The method of claim 1, wherein afterthe forming the first and second grooves, the mask layer overhangs thefirst groove and the second groove.
 4. The method of claim 1, whereinthe second dielectric layer includes two or more dielectric layers. 5.The method of claim 4, wherein at least one of the two or moredielectric layers is conformally formed in the first groove and thesecond groove.
 6. A method for manufacturing a semiconductor device,comprising: forming metal wirings embedded in a first dielectric layer,the metal wirings including a first metal wiring, a second metal wiringand a third metal wiring, all extending in a first direction andarranged in a second direction perpendicular to the first direction;forming a first insulating layer over the metal wirings and the firstdielectric layer; forming a first mask pattern over the first insulatinglayer, the first mask pattern including a first opening and a secondopening, both extending in the first direction and having a first widthin the second direction, respectively, the first opening being separatedfrom the second opening; reducing the width of the first opening and thesecond opening, thereby forming a second mask pattern having a thirdopening and a fourth opening, with a second width smaller than the firstwidth, respectively; patterning the first insulating layer by using thesecond mask as an etching mask, thereby forming a fifth opening and asixth opening in the first insulating layer corresponding to the thirdopening and the fourth opening, respectively; forming a first groovecorresponding to the fifth opening between the first metal wiring andthe second metal wiring and a second groove corresponding to the sixthopening between the second metal wiring and the third metal wiring byetching the first dielectric layer through the fifth and sixth openings;and forming a second dielectric layer so that a first air gap is formedin the first groove and a second air gap is formed in the second groove,wherein a width of the fifth opening in the second direction is smallerthan a space between the first metal wiring and the second metal wiringin the second direction.
 7. The method of claim 6, wherein the formingthe first mask pattern includes: forming a first layer on the firstinsulating layer; forming a second layer on the first layer; forming aphotoresist pattern on the second layer; patterning the second layer andthe first layer by etching using the photoresist pattern as an etchingmask; and after the etching, removing the photoresist pattern and thesecond layer, thereby forming the first mask pattern by the patternedfirst layer.
 8. The method of claim 7, wherein the first layer and thesecond layer are made of different organic materials.
 9. The method ofclaim 8, wherein a crosslinked organic layer is formed on a surface ofthe patterned first layer.
 10. The method of claim 6, wherein thereducing the width of the first and second openings includes: forming ablanket spacer layer on the first mask pattern and the first insulatinglayer exposed in the first and second openings; performing anisotropicetching on the blanket spacer layer, thereby forming sidewall spacers onsidewalls of the first opening and sidewall spacers on sidewalls of thesecond opening so that the second mask pattern having the third openingdefined by the sidewall spacers and the fourth opening defined by thesidewall spacers is obtained.
 11. The method of claim 10, wherein theblanket spacer layer includes titanium oxide.
 12. The method of claim 6,wherein the width of the first opening is equal to or greater than thespace between the first metal wiring and the second metal wiring. 13.The method of claim 6, wherein after the forming the first and secondgrooves, upper surfaces of the first metal wiring, the second metalwiring and the third metal wiring are covered by the first insulatinglayer and are not exposed.
 14. The method of claim 6, wherein after theforming the first and second grooves, the first insulating layeroverhangs the first and second grooves.
 15. The method of claim 6,wherein the second dielectric layer includes two or more dielectriclayers.
 16. The method of claim 15, wherein at least one of the two ormore dielectric layers is conformally formed in the first and secondgrooves.
 17. The method of claim 6, wherein: the second dielectric layerincludes a first etch-stop layer, a cap layer and an interlayerdielectric layer, the first etch-stop layer is conformally formed in thefirst and second grooves, the cap layer is conformally formed on thefirst etch-stop layer, and a part of the cap layer in the first grooveis not covered by the interlayer dielectric layer.
 18. A semiconductordevice, comprising: a first dielectric layer disposed over a substrate;metal wirings embedded in the first dielectric layer, the metal wiringsincluding a first metal wiring, a second metal wiring and a third metalwiring, all extending in a first direction and arranged in a seconddirection perpendicular to the first direction; a second dielectriclayer disposed over the first dielectric layer and the metal wirings; aninsulating layer disposed between the first dielectric layer and thesecond dielectric layer; and a first air gap formed between the firstmetal wiring and the second metal wiring and a second air gap formedbetween the second metal wiring and the third metal wiring, whereinupper surfaces of the first to third metal wirings are fully covered bythe first insulating layer and are not in contact with the seconddielectric layer.
 19. The semiconductor device of claim 18, wherein: thefirst insulating layer includes a first opening above a space betweenthe first metal wiring and the second metal wiring and a second openingabove a space between the second metal wiring and the third metalwiring, the first insulating layer overhangs the space between the firstmetal wiring and the second metal wiring and the space between thesecond metal wiring and the third metal wiring, and widths of the firstand second openings in the second direction are smaller than widths ofthe space between the first metal wiring and the second metal wiring andthe space between the second metal wiring and the third metal wiring inthe second direction.
 20. The semiconductor device of claim 18, wherein:the second dielectric layer includes a first etch-stop layer, a caplayer and an interlayer dielectric layer, the first etch-stop layer isformed and the cap layer is formed on the first etch-stop layer, therebydefining at least sides and bottoms of the first and second air gaps,and a part of the cap layer is not covered by the interlayer dielectriclayer.